1. Field of the Invention
The instant disclosure relates to a magnetic lens; in particular, to a desktop electron microscope and a combined round-multipole magnetic lens thereof.
2. Description of Related Art
Please refer to FIG. 1 showing a schematic diagram of a conventional electron microscope. The electron microscope comprises an electron gun 11 and a plurality of lens 12, 13, 141, 15. The mentioned lens may be magnetic lens or electric lens. The lens 12, 13 may be focus lenses, the lens 141 may be an aberration correction lens (which is cooperated with the electron deflector 14), and the lens 15 is an objective lens. After passing the lens 15 and the detector 16, the electron beam 4 hits the target 3. The type of the electron microscope can be the scanning electron microscope (SEM) or the transmission electron microscope (TEM). Whatever the type of the electron microscope is, the design of the lens greatly affects the performance of the electron microscope.
In recent years, the requirements for image resolution become important due to the development of electron microscopy. After the invention of the aberration corrector, it has become possible to enhance the image resolution of the electron microscope to sub-angstrom. Non-rotational symmetric multipole lens are often used in the aberration correctors in electron optical system.
The conventional aberration corrector is usually constituted by a plurality of multipole magnetic lens or electric lens. The aberration correction of the electron microscope is usually obtained by using a series of multipole lenses, and each lens has its respective function, wherein the function of the dipole lens is deflecting the electron beam by acting as a deflector, the quadrupole lens is usually for correction of chromatic aberration by using four magnetic lens cooperated with a quadrupole electric lens, and the octupole lens can be used to correct spherical aberration. However, the utilized quadrupole lens and the octupole lens can introduce more aberrations, and the hexapole lens is needed for compensation. Referring to FIG. 2, for example, the conventional aberration correction lens group may comprise two hexapole lenses 101, 102 and two cylindrical lenses 103, 104, wherein f is the focal length. Therefore, in order to use the multipole lens, it usually needs to cooperate with a plurality of power supplies for providing multiple magnetic fields or electric fields. However, after the invention of the desktop electron microscope, a lens (or lenses) with smaller volume is needed for achieving the aberration correction function or other related functions.